High temperature furnace



March 1, 1966 J c. MCGUIRE ETAL HIGH TEMPERATURE FURNACE Filed Oct. 31

v m 0 o O\@ 0 o 0 N/ fl// EGQE i INVENTOR. wdish Joseph C. McGuire, Donald 0. 80

United States Patent M 3,238,288 HIGH TEMPERATURE FURNACE Joseph C. McGuire, White Rock, and Donald D. Bowdish, Espanola, N. Mex., assignors t0 the United States of America as represented by the United States Atomic Energy Commission Filed Oct. 31, 1963, Ser. No. 320,592

Claims. (Cl. 13-31) This invention relates to an electrical induction furnace and, more particularly, to an extremely compact and easily constructed furnace capable of attaining very high temperatures. The invention described herein was made in the course of, or under, a contract with the US. Atomic Energy Commission.

Induction furnaces are, of course, known to the prior art but such furnaces, unless of extremely bulky construction, are limited to temperatures of approximately 2000 C. The present invention permits temperatures on the order of 2800 C., is very compact and easily constructed so that it is extremely useful in the laboratory investigation of the properties of ceramic materials.

The present invention provides an inductive furnace in which a vacuum may be applied or through which any selected gas may pass comprising a tungsten tube enclosed in a quartz envelope, said tube being separated and supported in the envelope with a thoria insulation layer. If gas flows through the heated portion of the tube, the inlet and outlet lines are so positioned with respect to said furnace that the gas flows through the tungsten tube over the sample being studied and then back through the thoria insulation (between the quartz envelope and tungsten tube).

Accordingly, it is an object of this invention to provide an inductively heated furnace wherein samples may be studied at temperatures up to 2800 C.

It is a further object of this invention to provide a high temperature furnace wherein the heated sample may be in an environment of any selected gas or vacuum.

It is another objective of this invention to provide an inductive furnace capable of operation at 2800 C. which is of an extremely compact nature,

It is a further objective of this invention to provide an inductive furnace capable of operation at a tempera ture of about 2800 C. which is of extremely simple construction; so much so that the device may be constructed in any well-equipped laboratory.

These and other objectives and advantages of the apparatus will be apparent from the accompanying drawing in which the single figure is a vertical sectional view of an induction furnace embodying the invention.

Referring to the figure, the device embodies a tungsten tube 1 and a quartz envelope 2. Thoria insulation 3 is placed between the tungsten tube and quartz envelope so that it separates and supports the tungsten tube 1 in the quartz envelope 2. The thoria is placed around the area of the tungsten tube which is heated by the inductive coil 4. Hydrogen gas may be fed to the tungsten tube through inlet duct 5 in which case the hydrogen flows inside the tungsten tube through orifice 6 of the tungsten tube, through the thoria insulation and out at exhaust duct 7. If a vacuum environment is desired, duct 5 is closed off and the system evacuated through duct 7. Duct 7 is utilized for evacuation in preference to duct 5 so that any impurities in the system owing to outgassing of the thoria will flow through duct 7 rather than passing over the sample inside the tungsten tube. When using a flowing gas such as hydrogen, duct 5 is utilized as the inlet in preference to duct 7 for the same reason, i.e., the outgassed impurities from the thoria will not flow over the 3,238,288 Patented Mar. 1, 1966 sample inside tungsten tube 1 but will exhaust immediately through duct 7.

O-ring 8 provides a seal between the quartz envelope and tungsten tube so that flowing hydrogen will not bypass the sample inside tungsten tube 1. The inlet portion 9 is sealed to the quartz envelope 2 at 10 by a ground joint. Black sealing wax may be used to effectuate a better seal. The inlet portion 9 is provided with an optical flat window 11 so that the sample may be observed with a pyrometer. Placing of the pyrometer in this position yields the benefit that the tungsten tube 1 provides a black body condition for the observance of the sample in the inductively heated area of tungsten tube 1.

The thoria insulation 3 is preferably of relatively coarse particles, e.g., greater than mesh US. Standard Sieve Series. The small surface area of relatively coarse particles minimizes gas occlusion so that impurities are minimized during vacuum runs. Although it is not strictly necessary, a material such as metal turnings may be provided betwen the tungsten tube and quartz envelope and betwen the thoria and -O-ring. This material would serve a two-fold purpose: First, it would provide a thermal barrier between ground joint 10 and the heated portion, and second, it would prevent migration of the thoria particles to the cooler end.

The materials embodied in the furnace are essential to its proper operation. The envelope should be constructed of quartz in preference to another ceramic material since its coeflicient of expansion is lower by an order of magnitude than other ceramic materials. This provides the necessary stability against thermal shock. The tungsten tube and thoria insulation is the only metal-metal oxide combination known to be compatible at the temperatures of interest. The choice of materials yields the beneficial advantage that even though the heated gas is flowing through the thoria between the tungsten tube (operated at 2800 C.), and the quartz envelope (which is useful only to about 1160 C.), the quartz envelope is not heated beyond its temperature limit.

In the particular embodiment shown in the drawing, the tungsten tube is of /z-inch inside diameter with a 20- mil thick wall. However, it should be understood that there is nothing at all critical in these dimensions. Actually it might be beneficial to have a thicker tungsten tube (which is not easily fabricated as a thin tube) since the inductive coil 4 primarily heats the tungsten tube rather than the sample within the tungsten tube. Accordingly, it is not necessary that the sample to be heated to be constructed of a conductive material. The device is equally useful for insulators such as ceramics and inductors such as metals.

When operating under vacuum, the inductive coil may be of as little capacity as 6 kilowatts in order to obtain an operating temperature of 2800 C. If a flowing gas is utilized, the inductive coil should be 10 kilowatts in order to obtain the 2800 C. operating temperature. The flowing gas condition is obtained by pressurizing the inlet duct 5 to slightly above atmospheric and discharging the gas through duct 7 to atmospheric pressure.

It will be noted from the above description and drawing that the pressure across the tungsten tube is always at a point of near equalization so that the strength, thickness and uniformity of the wall is not of importance.

It will be apparent from the above description and drawing that many modifications of the described embodiment would be within the spirit and scope of the invention. Consequently, the invention should be limited only by the following appended claims.

What is claimed is:

1. A high temperature inductive furnace comprising an inductive coil, a quartz envelope, said quartz envelope having inlet and outlet apertures, a tungsten tube enclosed within said quartz envelope, said tungsten tube separated and supported from said envelope at the coil end of the furnace by thoria insulation and sealed at the cold end of the furnace by an O-ring between said tube and said envelope, an optical flat window at the cold end of the furnace, metal turnings filling the annular regions formed by the tungsten tube and the quartz envelope between the O-ring seal and the thoria packing, said tungsten tube having orifices at both the cold and hot ends.

2. A high temperature inductive furnace comprising an inductive coil, a quartz envelope, said quartz envelope having inlet and outlet apertures, a tungsten tube enclosed within said quartz envelope, said tungsten tube to be separated and supported from said envelope at the coil end of the furnace by thoria insulation and sealed at the cold end of the furnace to said quartz envelope, said tungsten tube having an orifice at the coil end.

3. A high temperature inductive furnace as in claim 2 wherein an optical flat Window is provided at the cold end of the furnace.

References Cited by the Examiner UNITED STATES PATENTS 1,328,336 1/1920 Northrup 13-27 1,892,653 12/1932 McKenna 13-27 X 2,686,211 8/1954 Cargill 13-27 2,707,719 5/1955 Leibowitz 1331 2,754,347 7/1956 Wronghton et al. 1327 2,790,840 4/1957 Simnad et al. 1331 2,930,098 3/1960 Emeis 2l9--10.67

0 L. H. BENDER, Assistant Examiner.

RICHARD M. WOOD, Primary Examiner. 

1. A HIGH TEMPERATURE INDUCTIVE FURNACE COMPRISING AN INDUCTIVE COIL, A QUARTZ ENVELOPE, SAID QUARTZ ENVELOPE HAVING INLET AND OUTLET APERTURES, A TUNGSTEN TUBE ENCLOSED WITHIN SAID QUARTZ ENVELOPE, SAID TUNGSTEN TUBE SEPARATED AND SUPPORTED FROM SAID ENVELOPE AT THE COIL END OF THE FURNACE BY THORIA INSULATION AND SEALED AT THE COIL END OF THE FURNACE BY AN O-RING BETWEEN SAID TUBE AND SAID ENVELOPE, AN OPTICAL FLAT WINDOW AT THE COLD END OF THE FURNACE, METAL TURNINGS FILLING AN ANNULAR REGIONS FORMED BY THE TUNGSTEN TUBE AND THE QUARTZ ENVELOPE BETWEEN THE O-RING SEAL AND THE THORIA PACKING, SAID TUNGSTEN TUBE HAVING ORIFICES AT BOTH THE COLD AND HOT ENDS. 